WO2003078320A1

WO2003078320A1 - Thin silica film and silica-titania composite film, and method for preparing them

Info

Publication number: WO2003078320A1
Application number: PCT/JP2003/003326
Authority: WO
Inventors: Hiroki Okudera; Toru Nonami
Original assignee: National Institute Of Advanced Industrial Science And Technology
Priority date: 2002-03-19
Filing date: 2003-03-19
Publication date: 2003-09-25
Also published as: AU2003227187A1; US20050175852A1; DE10392399T5

Abstract

A method for preparing a thin silica film having a high density and being excellent in the transmittance of light on a substrate having an arbitrary shape and arbitrary surface characteristics; a method for controlling the surface roughness of the thin silica film; a production method for a silica-titania composite film; a composite film and a composite structure exhibiting a photocatalyst action produced by the production method.

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a thin film, a thin film and a titania composite film, and a method for producing them

The present invention relates to a novel method for producing a silica thin film and a composite structure, and more particularly, to a method for forming a film on a substrate surface having arbitrary surface characteristics and surface shape and controlling the film thickness. A new film forming method capable of forming a uniform and high quality silica thin film of a predetermined thickness on a substrate, and a high light transmission having a silica thin film formed by the method on a surface layer. The present invention relates to a composite structure having properties such as properties. This silica film is an electrical insulating film, a high-purity protective film using high strength, an optical waveguide forming film using high translucency, a low-reflection coating film using low refractive index, and fine defects on the substrate surface. It can be used in various ways as a repair film for repairing and recovering smoothness, an undercoat film for suppressing element diffusion from the substrate, a surface treatment film for modifying the substrate surface to an arbitrary surface roughness, and the like.

The present invention also relates to a novel silica-titania composite film, a method for producing the same, and a composite structure. More specifically, the present invention has one or more metal compound films containing a metal different from titanium as a component. The present invention also relates to a composite film having a titanium oxide thin film composed of a crystalline anode phase as the outermost layer, a method for producing the composite film, and a composite structure. INDUSTRIAL APPLICABILITY The present invention is useful as a method for producing a composite film in which a uniform and high-quality titania thin film is formed on an arbitrary substrate in a low temperature range of about 35. In addition, the composite membrane is used for environmental purification materials such as wastewater treatment and water purification using photocatalytic activity, antifouling coating using strong hydrophilicity, coherent color developing film using transparency, photocatalytic activity and transparent Photocatalytic window glass utilizing characteristics that combine properties, and optical waveguide type utilizing a high refractive index It can be used for various purposes such as film formation. Background art

Conventionally, as a chemical method for forming a silica thin film on a substrate surface, for example, a sol-gel method, a sputtering method, an LPD method and the like are well known. Among them, the sol-gel method prepares a partially hydrolyzed stabilized silica sol by adding a reaction catalyst, a stabilizer and the like to an alcohol solution of silicon alkoxide, and diving and spinning the solution as a coating solution. This is a method in which a coating is applied to the surface of a substrate by a method such as the above, a hydrolysis and a polymerization reaction are performed on the surface of the substrate, and a film is formed by heating and firing. The sputtering method is a method in which a substrate is fixed in a vacuum container, and silicon or a silicon compound vaporized by various methods is deposited on the substrate surface in the container to form a silica thin film on the substrate surface. . The LPD method is a method of forming a silica thin film on the surface of a substrate by precipitating silicon fluoride dissolved in the solution using the change in the degree of supersaturation in an aqueous solution and attaching the precipitated silicon fluoride to the surface of the substrate.

However, the following points are pointed out as problems of these conventional technologies. First, the sol-gel method is a method that can form a film at a low temperature in a relatively short time, but usually has a problem that it is difficult to maintain uniformity of the film. In addition, organic substances such as a stabilizer tend to remain in the silica forming the film, and high-temperature baking is required to remove them. In addition, the acid gas released during firing has an adverse effect on the firing apparatus. The sputtering method has problems that it is difficult to form a film on a surface having a complicated shape, and the reaction apparatus is complicated, expensive, and expensive. The LPD method has a problem that the process is complicated and that water and the like easily remain in the silica forming the film.

Also, a method for producing a silica thin film utilizing hydrolysis of a metal alkoxide The following can be cited as relevant items.

1) Japanese Patent Application Laid-Open No. 9-295058 "Method for producing silica thin film"

However, methods utilizing hydrolysis of metal alkoxides have not been proposed for 1) a method for strictly controlling the film thickness, 2) cannot control the surface roughness, and 3) the substrate surface is hydrophobic. There is a problem that the method of coating in certain cases is not presented.

Conventionally, chemical methods for forming a titania thin film on a substrate surface include, for example, a coating method, a sol-gel method, a chemical vapor transport method, a self-assembled monolayer film method, a Langmuir-Brochet method, and sputtering in a vacuum. And a film formation method using a new chemical reaction different from the sol-gel method are known. Among these, first, the coating method is a method of applying amorphous or crystalline anatase phase fine particles to a substrate together with a binder. In the sol-gel method, a stabilized titania sol obtained by partially hydrolyzing an alcohol solution of titanium alkoxide by adding a stabilizer is prepared, and the resulting solution is applied as a coating solution to a substrate surface by diving, spinning, or the like, and then dried. This is a method for forming a stable amorphous thin film by performing a dehydration polycondensation reaction on a substrate surface. In this method, if necessary, the above-mentioned amorphous film is transformed into a crystalline anatase phase by heating and firing. In the chemical vapor transport method, a vaporized titanium compound is introduced into a substrate fixed in a reaction vessel, and a titania film is formed on the substrate surface by utilizing a chemical bond between the substrate surface and the gas. It is a method of forming. At this time, the crystalline anatase phase is formed on the surface of the substrate by heating the substrate. The self-assembled monolayer method is similar to the chemical vapor transport method, in which a liquid phase or a gas phase containing a titanium compound is introduced into a substrate fixed in a reaction vessel and the surface of the substrate is introduced. This is a method of forming a titania film on the surface of a substrate by utilizing a chemical bond between a monomolecular film formed on the substrate and titanium. Langmuir Brossi The method involves forming a film by spreading a hydrophobic liquid, in which amorphous titania or crystalline anatase phase particles are suspended, on water in which it has been allowed to stand, and scooping the film on the surface of the substrate using a technique such as diving. It is.

In the sputtering method, a substrate placed in a high-vacuum reaction chamber is heated to increase the reactivity of the substrate surface, and titanium atoms or titanium oxide complex molecules are heated in the reaction chamber using a technique such as heating or laser irradiation. This is a method in which the substrate surface is covered with amorphous titania or a crystalline analog phase as in the chemical vapor transport method described above. Further, a film forming technique has been developed in which a new coating solution is prepared by a different kind of chemical reaction from the above-mentioned sol-gel method, and an anatase phase titania thin film is formed by baking after coating. According to this film forming technique, a coating solution is applied to a substrate, dried, and then heated at 400 to 500: to obtain an analog-phase titania thin film.

However, the weather resistance of the film produced by the above coating method depends on the weather resistance of the binder, and the stronger the photocatalytic activity of the crystalline anase phase, the faster the deterioration of the binder due to this. . The sol-gel method is a method that can form a film at a low temperature in a relatively short time.However, 1) it takes time to prepare a sol solution for coating, and 2) it is difficult to prepare and apply a sol solution in the air. 3) Organic substances are likely to remain in the titania forming the film, and in order to transfer the phase constituting the film to the crystalline anatase in order to exhibit the photocatalytic function, baking at a high temperature of 600 ° C or higher is usually required. And 4) diffusion of elements from the substrate due to heating hinders crystallization to a crystalline anode phase.

The Langmuir-Brochet method requires that the surface of the substrate be a hydrophobic and smooth flat surface. As for the chemical vapor transport method and the sputter method, the size of the substrate is limited and the On a rough surface, film formation is difficult, and there is a problem that versatility is poor in that the possibility of film formation depends on the heat resistance of the substrate and the surface characteristics of the substrate. Moreover, the reactor is complicated, expensive, and expensive. The self-assembled monolayer method has a problem that the processing procedure of the substrate is complicated and the versatility is poor. Furthermore, in the technique of forming an analog phase titania thin film by a chemical reaction different from that of the sol-gel method, heating is performed at 400 ° C or more to obtain a target analog phase titania thin film. Although a process is required, it is desired that the heating temperature be lower in consideration of the heat resistance limit of the substrate. Disclosure of the invention

Under these circumstances, the present inventors have made intensive studies with a view to developing a new film forming technique capable of drastically solving the problems of the above-mentioned conventional technology in view of the above-mentioned conventional technology. As a result, the low-density silica colloid with a diameter of 1 to 30 nm is generated in the liquid by the hydrolysis of silicon alkoxide, and the film formation process in the liquid by adhesion to these substrates and dehydration polycondensation It has been found that the desired object can be achieved by optimizing and controlling those processes, and further studies have been made to complete the present invention. That is, the first aspect of the present invention solves the above-mentioned problems of the prior art, and

) A method for producing a silica thin film capable of forming an amorphous silica thin film on a substrate surface of any shape irrespective of hydrophilicity or hydrophobicity; 2) a method for controlling the surface roughness of the silica thin film; ) A method of strictly controlling the thickness of the silica thin film by setting a reaction time.

Another object of the present invention is to provide a method for forming a uniform and high-quality silica thin film on a substrate by the above method.

Further, the present invention provides a highly transparent silica thin film obtained by forming a silica thin film obtained by the above method on a surface layer of an arbitrary structure and forming a composite on the surface layer. It is an object of the present invention to provide a composite structure having: Furthermore, in view of the above-mentioned prior art, the present inventors have drastically solved the above-mentioned problems of the prior art, and particularly, have produced a uniform and high-quality titanium oxide film in a low temperature range of about 350. As a result of intensive research aimed at developing a new film forming technology that enables the formation of a silica film on a substrate under specific conditions, a titanium oxide film is formed under a specific condition. It has been found that the intended purpose can be achieved by constructing a titania composite membrane, and further studies have been made to complete the present invention.

That is, the second aspect of the present invention solves the above-mentioned problems of the prior art, and provides a substrate surface of an arbitrary material having an arbitrary shape and surface characteristics in a much lower temperature range than the conventional method. An object of the present invention is to provide a novel method for producing a crystalline anatase phase thin film that can be formed into a thin film.

Another object of the present invention is to provide a novel high-functional silica-titania composite film having a photocatalytic action, which is uniform and high-quality, produced by the above method.

Still another object of the present invention is to provide a composite structure having a photocatalytic action, having the composite film formed on the surface layer of an arbitrary structure to form the composite film on the surface layer. Next, the first embodiment of the present invention will be described in more detail.

As a result of various studies to solve the above-mentioned problems in the prior art, the present inventors have found that: 1) a precipitate product of amorphous silica formed by hydrolysis of silicon alkoxide having a diameter of several tens of secondary particles as aggregation stabilization of unstable primary particles of nm or less.2) During the process of generating precipitated products, if any object is immersed in the reaction solution, If the surface of the body is hydrophilic, the primary particles will adhere to the surface of the body and form a uniform thin film (Fig. 1). 3) The silica thin film thus obtained is dense, and is heated and fired after drying. And 4) if the surface of the substrate is hydrophobic, the primary particles and the secondary particles formed by aggregating the primary particles in the reaction solution, It was found that Brownian motion and van der Waals coupling in the solution caused the film to adhere to the substrate surface with a low probability, and that they formed a uniform but large surface roughness thin film (Fig. 2). FIG. 1 schematically shows a process of forming a silica thin film on a substrate having a hydrophilic surface and a smooth thin film obtained by the process. FIG. 2 schematically shows a process of forming a silica film on a substrate having a hydrophobic surface and a thin film having a large surface roughness obtained by the process.

The present invention is based on the discovery of such a new fact. The present invention provides a method of immersing a substrate in a solution composed of silicon alkoxide, alcohol, ammonia, and water at a temperature of room temperature or lower. The present invention relates to a novel method for producing a silica thin film, wherein a silicide force generated by hydrolysis of an alkoxide is attached to a substrate surface. The present invention broadly relates to a method for forming a silica thin film on the surface of a substrate, a method for controlling surface roughness by controlling the surface state of the substrate, and a method for forming a silica thin film obtained by the method on a surface layer. And a composite structure having the same.

In the present invention, the solution composed of silicon alkoxide, alcohol, water and alkali used for forming the thin film includes: 1) silicon alkoxide, preferably silicon methoxide, silicon ethoxide, silicon isopropoxide, silicon Butoxide, 2) alcohol as a solvent, preferably methanol, ethanol, isopropanol, butanol, and 3) water required for hydrolysis and a catalyst for promoting hydrolysis Alkali, preferably ammonia, You. These are preferably mixed in the following concentration ranges.

1) Silicon alkoxide: 0.05 to 0.5 mol / l

2) Alkali (ammonia): 0.5 to 5.0 m o 1/1

3) Water ::! ~ L Omo lZ l

Next, an outline of the method of the present invention is shown in FIG.

Preferably, the silica film of the present invention uses silicon alkoxide, alcohol, ammonia, and water, and after mixing and stirring a predetermined amount thereof, immerses the substrate therein and sets the temperature at a predetermined temperature for several minutes to several minutes. It is produced by holding for 10 hours.

Whether or not a film is formed on the substrate surface is governed by the rate of formation of silicon acid generated by hydrolysis of silicon alkoxide and the polymerization state, and the ratio of silicon alkoxide to water in the prepared solution composition Is important. The formation of a film on the substrate surface is due to the attachment of transient primary particles of 1 to 30 nm in diameter generated during the hydrolysis reaction. Therefore, if the surface of the substrate is hydrophilic, the primary particles adhere to the surface of the object, and the film becomes uniform.If the surface of the substrate is hydrophobic, the probability of adhesion of the primary particles decreases, and aggregation occurs. Since the secondary particles, which are substances, adhere, the surface of the film becomes uneven. For this reason, the surface characteristics of the substrate are important for the desired film surface shape.

In the present invention, for example, metal, glass such as soda lime glass and silicon glass, plastics such as polyethylene and polystyrene, and silicon rubber are used as the substrate. However, the present invention is not limited to these, and may be any one. The surface of the substrate may be hydrophilic or hydrophobic. For example, the surface of the substrate may be hydrophobized by surface treatment by chemical modification represented by fluorine treatment. The surface state of the substrate may be smooth or uneven. The optimum mixing ratio of the above components that form a film on the surface of a hydrophobic substrate is the mixing ratio at which monodisperse spherical silica particles as secondary particles are formed in a solvent.

The optimum mixing ratio of the above components that forms a film on the surface of the hydrophilic substrate is 1) the mixing ratio at which monodisperse silica particles are formed as secondary particles in the solvent, and 2) the mixing ratio is 1). Therefore, the mixing ratio has a slightly lower hydrolysis rate, that is, the mixing ratio in which the water concentration or the ammonia concentration is lower than the condition under which monodisperse silica particles as secondary particles are formed in the solvent. If a uniform film is not formed due to rapid hydrolysis, hydrolysis is suppressed by setting the treatment temperature low, and a uniform film can be obtained. Therefore, in the present invention, the concentration of silicon alkoxide is not important, and when the concentration of silicon alkoxide is reduced, the concentration of water or ammonia is increased, and a uniform silica film is obtained by setting a long reaction time. Can be formed.

When the silicon alkoxide concentration is increased, a uniform silica thin film can be formed by lowering the water concentration or the ammonia concentration and lowering the reaction temperature. In the present invention, as described above, as the silicon alkoxide, one or more of silicon methoxide, silicon ethoxide, silicon isopropoxide, and silicon butoxide can be used. As the solvent, one or more of methanol, ethanol, isopropanol and butanol can be used. Among them, silicon tetraethoxide is preferable as the silicon alkoxide, and ethanol or isopropanol is preferable as the solvent. Its concentration is 0.05-0.5 mol Zl, preferably 0:!-0.2 mo 11. Water is needed to cause the hydrolysis of silicon alkoxides to produce silicon acids. The amount is silicon alkoxide The molar ratio is in the range of 1 to 100.

In the present invention, the alkali is required as a catalyst that causes hydrolysis of silicon alkoxide to produce colloidal silicate. In the present invention, ammonia is preferably used as the alkali. The amount is in the range of 1 to 100 in molar ratio with respect to the silicon alkoxide. The holding temperature of the reaction solution during the film formation process may be below freezing or above room temperature, but is preferably 0 ° C. or more and 30 or less. In this case, the reaction may be performed in a closed vessel in order to prevent the solvent from volatilizing. It is necessary to keep the reaction solution in a dynamic state in order to promote the adhesion of the low-density silicate colloid to the substrate. In this case, as a method of maintaining the reaction solution in a dynamic state, the reaction solution is shaken, preferably, the reaction tank is shaken, the solvent is circulated, the substrate is vibrated, And the like, but are not limited to these. Further, these operation means are not particularly limited, and any means can be used. In the present invention, it is extremely important to keep the reaction solution in a dynamic state. When the reaction solution is allowed to stand, it is difficult to optimize the reaction conditions, and it is difficult to achieve the intended purpose. In the present invention, “maintaining in a dynamic state” means that the reaction solution is kept in a non-static state without standing.

In the present invention, by appropriately setting the reaction conditions, the film formation rate can be expressed as a logarithmic function of the retention time. Further, since the formation of the film is due to the transient attachment of the primary particles, the starting time of the immersion of the substrate in the reaction solution may be any time during the reaction is continued. Therefore, a desired film thickness can be obtained by appropriately setting the start time of immersion and the subsequent holding time. The film formation rate is proportional to the silicon alkoxide concentration in the solvent. Therefore, by adjusting the silicon alkoxide concentration, the same The film thickness can be controlled by the processing time. By making the surface of the substrate hydrophobic, the probability of transient primary particles adhering to the substrate surface is reduced, and at the same time, the probability of secondary particles, which are aggregates of primary particles, adhering to the substrate surface is increased. Can be. Therefore, the surface shape of the thin film can be controlled by increasing the hydrophobicity of the substrate surface. As described above, at this time, it is extremely important that the reaction solution is kept in a dynamic state as a film forming condition. Therefore, in the present invention, the shaking of the reaction vessel, the circulation of the solvent, or the substrate Is an important component. The amorphous silicon film obtained by the method of the present invention has a high density in a deposited state, and the drying process can be omitted. In addition, it shows sufficient hardness when dried at room temperature. The amorphous silica film obtained by the method of the present invention becomes insoluble in alcohol by drying, and a thicker film can be obtained by repeating this process. Further, by heating and sintering this, OH and alkyl groups remaining inside the structure of the amorphous silicon film obtained by the method of the present invention can be removed, whereby high-purity amorphous silica can be obtained. Can be formed.

The silica film of the present invention has excellent properties such as high translucency, high insulating properties, high density, and super water repellency (due to hydrophobicity). From this, the silica film can be formed on the surface of an arbitrary structure to be composited. As a result, a composite structure having the above properties can be produced. The silicon film of the present invention can be used, for example, as an insulating film, a low-reflection coating film, an optical waveguide forming film, a photoconductive material, an undercoat film, a surface treatment film, or the like. It can be applied to all kinds of composite structures such as films, optical glass, liquid crystal panels, cathode ray tubes, glass windows, protective covers, materials, electronic components, structures, etc. having this as a surface layer.

In the present invention, silicon alkoxide, alcohol, water and alkali The substrate is immersed in a solution consisting of the solution, and the silicon alkoxide is hydrolyzed in an alcohol solvent to form low-density colloidal silica of 1 to 30 nm in diameter. By maintaining the reaction solution in a dynamic state by any means during the process of forming the silica thin film, it is possible to promote the adhesion to these substrates and the film formation in the solution by dehydration polycondensation. As a result, a silica film having a uniform thickness and a predetermined thickness can be formed on the substrate in the liquid. In this case, the thickness of the silica film can be controlled by the silicon alkoxide concentration, the water concentration, the catalyst concentration, the treatment temperature, the treatment time, and the number of treatments. In addition, the surface shape of the thin film can be controlled by increasing the hydrophobicity of the substrate surface. The amorphous silica film produced by the above method has a uniform and high density, and by drying it at room temperature, high hardness can be added. By heating and baking this, a high-purity, high-density amorphous silicon film can be obtained. The silica film of the present invention has, for example, a property of improving the light transmittance of a glass substrate, as shown in Examples described later. The adhesion of the low-density gay acid colloid to the substrate and the dehydration polycondensation in the present invention will be described. Transient silicon acid generated by hydrolysis of silicon alkoxide repeatedly condenses and redissolves in a liquid. Of the transient silicon acid colloids formed by condensation, only those that have a reduced surface area / volume ratio due to collision with each other escape from re-dissolution and become a solid phase. This transitional siliconic acid colloid is constantly generating and dissolving during the course of the reaction, and its size is proportional to the degree of supersaturation of the dissolved siliconic acid. Thus, in the present invention, as long as the above-mentioned reaction is in progress, the start and duration of immersion of the substrate can be arbitrarily set to form a silica film on the surface of the substrate. In addition, by maintaining the reaction solution in a dynamic state by, for example, relatively moving the solution and the substrate, even if the surface of the substrate is hydrophobic, transient silicon oxide colloid can be formed on the surface of the substrate. Adhere to It becomes possible. Next, the second embodiment of the present invention will be described in more detail.

The present inventors have conducted intensive studies to solve the above-mentioned problems of the prior art, and as a result, 1) a titanium alkoxide hydrolyzed in a solution composed of titanium alkoxide, alcohol, and water has a diameter of several tens of nanometers. The following transient primary particles of colloidal titanate are formed.2) By immersing the substrate in a solution consisting of titanium alkoxide, alcohol and water, the The present inventors have found that a titania thin film is formed on the surface of a substrate by one-loose bonding, and that a thin film of titania is formed on the surface of the substrate. By placing a metal compound film containing a metal element, for example, an amorphous silica thin film, the diffusion of elements from the base material to the titania thin film is reliably inhibited, thereby providing a uniform and uniform film. A high-quality titania thin film can be formed, and further, by heating and firing the composite film at about 350, titania, which is the outermost layer of the composite film, can be easily transferred to a crystalline phase. It is possible to find out.

The present invention relates to a metal compound film such as an oxide film of a metal other than titanium having a uniform thickness of 0.01 to 100 m, preferably a non-metallic film, between the surface of the substrate and the titanium oxide. A composite film having a crystalline silicon film, wherein a uniform titanium oxide having a thickness of 0.01 to 100 m as the outermost layer is a crystalline anatase phase. Further, the present invention relates to a method for producing the composite film, and a highly functional composite structure having the composite film on the surface.

The composite film according to the present invention, wherein the outermost layer is a crystalline anamorphic titania thin film Basically, a) the substrate surface is coated with one or more layers of a metal compound film of a metal other than titanium, for example, a metal oxide thin film.b) The substrate of a) is coated with an amorphous titania thin film. C) baking the above b) at a temperature of 300 or more. A metal compound film of a metal other than titanium, for example, an oxide thin film is provided between the base and the titania thin film to inhibit the diffusion of elements between the base and the titania thin film, thereby achieving uniform and high-quality titania. It is formed for the purpose of enabling a thin film to be formed. For these purposes, it is preferable to use a crystalline or silicic film, and an amorphous silica film may be used as long as the above object can be achieved. However, the present invention is not limited thereto, and compounds having low reactivity at high temperatures, for example, silicon compounds, preferably silicon nitride, other nitrides, etc., may be used as long as they have the same effect. be able to.

For the preparation of the amorphous silica film, preferably, the substrate is immersed in a solution comprising silicon alkoxide, alcohol, water and ammonia, and the silicon alkoxide is hydrolyzed to form amorphous silica on the surface of the substrate. Form a film. In this case, it is necessary to keep the reaction solution in a dynamic state (non-static condition). Thereby, a uniform and high quality silica thin film can be formed by optimizing the film forming process. When the target thickness is not achieved, this operation is repeated, and the obtained silica film-coated substrate is dried, and if necessary, a temperature of at least 300 and at most 100, preferably around 350 ° C. For example, a method in which the silica film is made to have a high density by heating and calcining in the above manner is used. However, it is not limited to these methods. This amorphous silica film is preferably further densified by heat treatment. By forming this densified amorphous silica between the substrate and the titania film, the diffusion of elements from the substrate to the titania thin film is reliably inhibited. This makes it possible to form a uniform, high-quality, highly durable titania film. When such an amorphous silica film is not formed, it is difficult to transfer the above-mentioned titania film to a high-purity crystalline analog phase, as shown in Examples described later. In the method of the present invention, in the method for producing an amorphous silica film, the formation of the silica film is not affected by the size, material, shape, surface hydrophilicity and hydrophobicity of the substrate. .

Therefore, the formation of the silica-titania composite film of the present invention composed of this silica film and the titania film bonded thereon also involves the size, material, shape and hydrophilic / hydrophobic properties of the substrate. It is not affected separately. This makes it possible to form a titania film on the surface of a substrate of any material having any shape and surface characteristics. In the present invention, examples of the substrate include, but are not limited to, metals, metal oxides, glasses such as soda lime glass and silica glass, plastics such as polyethylene and polystyrene, and silicone rubber. , Any of them. The surface state of the substrate may be smooth or uneven. The surface of the substrate may be hydrophilic or hydrophobic, and these properties are not particularly limited.

In the present invention, the formation of the amorphous titania thin film as a stage prior to the formation of the crystalline analog phase thin film is performed by immersing the substrate in a solution composed of titanium alkoxide, alcohol, and water and holding the substrate for a predetermined time. Thus, the titanium alkoxide is hydrolyzed to form a low-density titanate titanate having a diameter of 1 to 30 nm in the liquid, and the titanium oxide is attached to the surface of the substrate by adhesion to the substrate and dehydration polycondensation. An object film is formed, and when the target thickness cannot be achieved by one operation, this operation is repeated. The formation of the amorphous titania film is caused by the attachment of the transient colloidal titanate secondary particles having a diameter of several tens of nanometers or less generated in the solvent to the substrate surface. Therefore, the formation of the amorphous titania film is not affected by the size, material, shape, surface hydrophilicity or hydrophobicity of the substrate. Therefore, for example, prior to forming the amorphous titania film portion, the surface of the lower silica film portion can be chemically modified.

Whether a uniform and high-quality titania film is formed on the substrate surface depends on the polymerization state of titanic acid generated by the hydrolysis of titanium alkoxide and the transitional colloidal titanate having a diameter of tens of nanometers or less. It is governed by the particle generation power, and the ratio of titanium alkoxide to water is important in the prepared solution composition. Therefore, the concentration of titanium alkoxide is somewhat unimportant.Basically, if the concentration of titanium alkoxide is reduced, increase the concentration of water and set a long reaction time. By doing so, a titania film can be formed. In the present invention, as described above, as the titanium alkoxide, one or a mixture of two or more of titanium methoxide, titanium ethoxide, titanium isopropoxide, and titanium butoxide is preferably used. Titanium tetraethoxide or titanium tetraisopropoxide is used. As the solvent, one or a mixture of two or more of methanol, ethanol, isopropanol and butanol is used, and preferably, ethanol or isopropanol is used. The concentration range is preferably from 0.01 to 1.0 Omol Zl, and the desired concentration range is from 0.025 to 0.1 Imol Zl. Water is necessary to cause hydrolysis and the production of colloidal titanate. The amount is in the range of 1 to 100 in molar ratio to titanium alkoxide. The holding temperature of the reaction solution during the film formation process may be below the freezing point, but is preferably 0 ° C. or more and 100 ° C. or less. More preferably, it is around room temperature. In this case, the reaction is performed in a closed container to prevent evaporation of the solvent. It is preferred to do so.

The above reaction may be carried out in a stationary state, but it is preferable to keep the reaction solution in a dynamic state in order to obtain a uniform film. As a method for this, circulating the solution and using a substrate The reaction is preferably carried out in a shaking environment (non-static condition) by shaking or shaking the reaction tank. In the method of the present invention, the rate of film formation can be expressed as a logarithmic function of the retention time. In addition, the formation of the film is caused by the transient adhesion of colloidal titanate particles having a diameter of several tens of nanometers or less, which are generated by hydrolysis of titanium alkoxide. By properly setting the thickness, the film thickness can be strictly controlled. The amorphous titania film obtained in the present invention is fired at a temperature of at least 300 ° C. and at most 100 ° C., preferably at around 350 ° C., to form a high-purity, high-density crystalline anatase phase. Can be transferred. At this time, the ΔH and alkyl groups contained in the inside of the film structure can be removed, so that a composite film whose outermost layer is made of a highly pure crystalline anatase phase can be formed.

In the present invention, in a titanium alkoxide solution, a metal compound film containing a different metal different from titanium as a component, for example, a metal oxide film, preferably a substrate having one or more layers of a silica film on the surface is used. By immersing and hydrolyzing the titanium alkoxide, a low-density colloid of titanate having a diameter of 1 to 30 nm is generated in the liquid, and the titanium adheres to the surface of the substrate in the liquid by adhesion to the substrate and dehydration polycondensation. By optimizing these in the process of forming the oxide film, a uniform and high-quality titania film can be formed on the substrate. In the present invention, by forming the silica film portion below the titania film portion, the diffusion of elements from the substrate to the titania thin film can be reliably inhibited, whereby the uniform, high quality, high durability Of a titania film Becomes possible.

The method of the present invention makes it possible to produce a composite in which the titania film is formed on the surface of a substrate of any material having any shape and surface characteristics. Further, by firing the above-mentioned complex in a low temperature range of at least 300 and at most 100, preferably at around 350 ° C., it is possible to transform into a high-purity crystalline analog phase. . Transient titanic acid generated by the hydrolysis of titanium alkoxide repeatedly condenses and redissolves in the liquid, and among the transient colloidal titanate colloids formed by condensation, they collide with each other and surface area z volume ratio Only those having a reduced size escape from re-dissolution and become a solid phase. This transitional colloid of titanate constantly repeats generation and dissolution during the course of the reaction, and its size is proportional to the degree of supersaturation of the dissolved titanic acid. The present invention, based on the discovery of this fact, has realized that a titania film can be formed on the surface of a substrate even when the start and duration of immersion of the substrate are arbitrarily set as long as the reaction is in progress. . FIG. 6 shows an outline of the method for producing a composite membrane of the present invention. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic diagram of a process of forming a smooth film on a substrate in the present invention. FIG. 2 shows a schematic diagram of a process of forming a film having a large surface roughness on a substrate in the present invention.

FIG. 3 shows the outline of the method of the present invention.

Figure 4 shows the relationship between the thickness of the silica film and the reaction time.

Figure 5 shows the results of measuring the transmittance of glass with an ultraviolet-visible light spectrophotometer.

FIG. 6 shows an outline of the method for producing a composite membrane of the present invention. Figure 7 shows the results of X-ray powder diffraction of the composite membrane (the diffraction line at a diffraction angle of 25 degrees indicates the presence of a crystalline anase phase).

Figure 8 shows the results of X-ray powder diffraction of the composite membrane (the diffraction line at a diffraction angle of 25 degrees indicates the presence of the crystalline anatase phase).

FIG. 9 shows the relationship between the thickness of the titania film and the reaction time.

FIG. 10 shows the relationship between the thickness of the titania film formed on the hydrophilic and hydrophobic substrates and the reaction time.

FIG. 11 shows the results of measuring the light transmittance of glass in the ultraviolet-visible light region. BEST MODE FOR CARRYING OUT THE INVENTION

Next, an example of the first aspect of the present invention will be specifically described.

Example 1

As a substrate, a silicon substrate whose surface is hydrophilic, a silicon substrate whose surface is chemically modified (fluorinated) with a 1H, 1H, 2H, 2H-perfluorodecyltrimethyloxysilane monomolecular film whose surface is strongly hydrophobic, It was used. A solution prepared by dissolving this in ethanol so that it becomes 0.11 mo 11 silicon tetraethoxylate at the time of reaction, and adding ethanol 3.Omo 1/1 and ammonia 1. The substrate was immersed in the former solution. While the former vessel was shaken to keep the reaction solution in a dynamic state, the latter was added thereto, the vessel was sealed with a film, and the vessel was further shaken to keep the reaction solution in a dynamic state. While maintaining the temperature at 20 ° C.

After a predetermined time had elapsed, the substrate was taken out, washed with 12 Oml of ethanol and 0.648 ml of water, and dried at 70 t. The thickness of the obtained silica film was adjusted with an atomic force microscope (AFM). Beta. The film thickness was expressed by the following equation as a function of the time t (min) from 60 minutes to 240 minutes in the reaction time (Fig. 4).

On untreated silicon plate: d (nm) = 30 log (t)-8.8 On hydrophobically treated silicon plate: d (nm) = 33 log (t)-36 Also, silica on silicon single crystal substrate The surface roughness of the film was 1 nm in RMS roughness. The surface roughness of the fluorine-treated silicon single crystal substrate was 10 to RMS roughness: L 4 nm. Example 2

In Example 1, the substrate was soda lime glass, and both surfaces of the glass plate were covered with an amorphous silica film having a thickness of 137 nm. The transmittance of this sample was measured with an ultraviolet-visible light spectrophotometer. In comparison with the untreated substrate, it was found that the coating of the amorphous silicon film improved the light transmittance (Fig. 5). Next, an example of the second aspect of the present invention will be specifically described.

Example 3

(1) Formation of silica thin film

In this example, a soda lime glass plate was used as a base. A silica film was formed by the following procedure. A solution prepared by dissolving this in ethanol so that silicon tetraethoxide becomes 0.22 mo 1/1 at the time of reaction, and these were added so that water 6.Omol Z and ammonia 2.Omol Zl during the reaction. A solution dissolved in ethanol was prepared, and the substrate was immersed in the former. After the former was shaken and the reaction solution was kept in a dynamic state, and the latter was added thereto, the container was sealed with a film and held at 20 with shaking. After 2 hours, the substrate was taken out, washed with a mixture of 120 ml of ethanol and 0.648 ml of water, dried at 70, and baked at 35 for 48 hours. did. As a result of examining the thickness of the obtained silica film with an atomic force microscope (AFM), the thickness was 0.12 ^ m. The surface roughness of the silica film was 1 nm in RMS roughness.

(2) Formation of titania film

Next, a titania film was formed by the following procedure. A solution in which 1.35 g of titanium ethoxide and 100 ml of isopropanol and a solution in which 0.648 ml of water and 20 ml of isopropanol were mixed were prepared, and the substrate was immersed in the former. After the former container was shaken and the reaction solution was shaken, and the latter was added thereto, the container was sealed with a film and held at 20 while shaking.

After 4 hours and 8 hours, the substrate was taken out and dried at 70 ° C. for 2 hours. As controls, 1) a soda-lime glass substrate having no silica thin film on the surface, and 2) a soda-lime glass having a silica thin film on the surface but not firing at 350 ° C after the formation of the silica thin film and before the formation of the titania thin film. The same processing was performed on the substrate and the substrate. After that, these samples were heated and fired at 350 ° C.

(3) Result

A part of the unfired titania thin film was peeled off, and the thickness was measured with an atomic force microscope. As a result, the film thickness was 0.09 m and 0.18 m, respectively, for the films subjected to the film forming treatment for 4 hours and 8 hours. Next, the presence or absence of a crystal phase was examined using an X-ray diffractometer. As a result, no diffraction line due to the crystal phase was observed for any of the samples. Next, the heat-fired sample was examined for the presence of a crystal phase by an X-ray diffractometer, and it was found that a silica thin film was provided between the soda lime glass and the titania thin film. Diffraction lines due to the crystalline anatase phase were observed only in the case where the thickness of the tania film was 0.18 m and the silica thin film was fired at 350. (Fig. 7).

Even though the silica thin film was fired at 350 :, the diffraction line due to the crystalline anamorphous phase was observed for the titanium film with a thickness of less than 0.09 m. Did not. With respect to the silica thin film, the same results were obtained when the firing conditions were set at 450 and 10 hours.

From these experiments, it is found that the thicker the silica film, the more the diffusion of elements from the substrate is hindered. Therefore, even if the titania film is thin, it can be transferred to the anatase phase. It was found that the phase could be changed. Example 4

A silica film and a titania film were formed in the same manner as in Example 3 above. When the thickness of the silica film was 0.24 / m, the titania film formation time was 4 hours. Regarding the titania film with a thickness of 0.09 / m, the silica film thickness of 0.24 m, after firing at 350 at 48 hours, is due to the crystalline anaphase. Diffraction lines were observed (Fig. 8). Example 5

In the same manner as in Example 3 above, titanium alkoxide was used as titanium isopropoxide, and a silica glass plate was used instead of the silica film.The titania film formation time was 6 hours, and the titania film thickness was 0. Diffraction lines attributable to the crystalline phosphor phase were also observed at 14 m . The firing temperature at this time was lower than that of Examples 3 and 4, and was 300. Example 6

A titania film was formed on a substrate in the same manner as in Example 3 described above, and the film thickness of the titania film when a silicon plate and a soda lime glass plate were used as the substrates was examined. As a result, it was found that the titania film thickness was expressed by the following equation as a logarithmic function of the reaction time t (min) (Fig. 9).

On a silicon plate: d (nm) = 232 l o (t)-45 1 On a soda lime glass plate: d (nm) = 243 l o g (t)-47 5 Example 7

In Example 3, the solvent was ethanol, a silicon plate was used as a hydrophilic substrate, and a 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane monomolecular film whose surface was strongly hydrophobic was used as a strongly hydrophobic substrate. A titania film was formed in the same manner as in Example 3 except that a chemically modified (fluorinated) silicon plate was used as a substrate. As a result of measuring and examining the thickness of the obtained titania film with an atomic force microscope, it was found that the film thickness was represented by the following equation as a logarithmic function of the reaction time t (min) (FIG. 10). ).

On untreated silicon plate: d (nm) = 1 4 1.89 1 og (t) 1 1 3 1 .1 7

On hydrophobically treated silicon plate: d (nm) = 1 2 7. 2 3 1 og (t) 1 1 1 9. 3 3 Example 8 The composite film having a silica film thickness of 0.12 m, a titanium film thickness of 0.18 m, and a crystalline anamorphic phase produced in Example 3 was bonded to one surface. For soda-lime glass, the light transmittance in the ultraviolet-visible light range was measured. As a result, it was found that the decrease in light transmittance over the entire visible light region was as low as about 10% (FIG. 11). Further, when the photocatalytic activity of this composite film was examined by a conventional method, it was found that the composite titania film had an excellent photocatalytic effect. Industrial applicability

As described in detail above, the present invention relates to a novel method for producing a silica thin film and a composite structure. The present invention has the following special effects.

(1) According to the method for producing a silica thin film of the present invention, an amorphous silica thin film is formed on a substrate having an arbitrary surface property and an arbitrary surface shape by controlling the film thickness. A uniform and high quality silica film having a predetermined film thickness can be formed thereon.

(2) If the temperature is lower than the heat-resistant temperature of the substrate, high-purity can be achieved by removing the impurities remaining inside the film by heating and firing.

(3) This silica thin film uses an electrical insulating film that uses electrical insulation, a high-purity protective film that uses high strength, an optical waveguide forming film that uses high translucency, and fine irregularities on the surface. It can be diversifiedly used for industrial applications such as a low-reflection film that has been repaired and a repair film that repairs minute defects on the substrate surface.

(4) It is possible to provide a composite structure having high light transmittance, having a silica thin film obtained by the above method in a surface layer.

Further, the present invention relates to a silica-titania composite film, a method for producing the same, and a composite structure. According to the present invention, the following special effects can be obtained. Is played.

(1) According to the method for producing a silica-titania composite film of the present invention, if the heat resistance temperature of the substrate is 300 ° C. or higher, the crystalline anode phase thin film can be formed in any surface state and in any desired state. It can be formed on a surface-shaped substrate.

(2) This crystalline analog thin film is used for environmental purification applications such as wastewater treatment and water purification treatment utilizing its photocatalytic activity, antifouling coating utilizing strong hydrophilicity, and coherent coloring film utilizing transparency. Suitable for use in surface decoration applications such as surface applications, living environment improvement applications such as photocatalytic functional window glass utilizing both photocatalytic activity and transparency, and industrial applications such as optical waveguide forming films using a high refractive index. Can be.

(3) It is possible to provide a composite structure having a photocatalytic action, wherein the composite film is formed on a surface layer.

Claims

The scope of the claims

1. A method for producing a silica thin film bonded to a substrate surface,

(1) immersing the substrate in a solution composed of silicon alkoxide, alcohol, water and alkali;

(2) Hydrolysis of silicon alkoxide in an alcohol solvent produces low-density gay acid colloid with a diameter of 1 to 30 nm in the liquid.

(3) forming a uniform silica thin film of a predetermined thickness on the substrate in the liquid by adhesion to the substrate and dehydration polycondensation;

(4) maintaining the reaction solution in a dynamic state during the film formation process,

A method for producing a silicon thin film.

2. The method according to claim 1, wherein the silicon alkoxide is at least one selected from the group consisting of silicon tetramethoxide, silicon tetraethoxide, silicon tetraisopropoxide, and silicon tetrabutoxide.

3. The method according to claim 1, wherein the alcohol as the solvent is at least one selected from the group consisting of methanol, ethanol, and isopropanol.

4. The method according to claim 1, wherein the silica film has a thickness of 1 nm to 10 / m.

5. The method according to claim 1, wherein the reaction solution is maintained in a dynamic state by shaking the reaction solution to promote the adhesion of the low-density colloidal colloid to the substrate.

6. The method according to claim 1, wherein the reaction solution is maintained in a dynamic state by circulating the solvent, vibrating the substrate, or shaking the reaction vessel.

7. The method according to claim 1, wherein the surface roughness of the thin film is controlled by setting the hydrophobicity of the substrate surface.

8. The method according to claim 1, wherein a predetermined film thickness is obtained by arbitrarily setting a start time of immersion of the substrate and a subsequent holding time.

9. The method according to claim 1, wherein the substrate is a substrate whose surface is hydrophobized by chemical modification represented by fluorine treatment, silicone rubber, acrylic resin, or cellulose.

10. A method for producing a silica thin film, comprising drying a silica thin film obtained by the method according to any one of claims 1 to 9.

11. The method according to claim 10, wherein the density of the film is arbitrarily set by a heat treatment after drying.

12. A composite structure having high light transmittance, comprising a silica thin film obtained by the method according to any one of claims 1 to 11 in a surface layer.

13. A method for producing a composite film having one or more metal compound films containing components of metals different from titanium and having a titanium oxide film on the outermost surface,

(1) A substrate having one or more layers of a metal compound film containing a metal different from titanium is immersed in a titanium alkoxide solution. (2) A liquid is obtained by hydrolyzing the titanium alkoxide. Produces low-density colloidal titanate of 1 to 30 nm in diameter,

(3) coating the surface of the substrate with titanium oxide in a liquid by adhesion to the substrate and dehydration polycondensation;

A method for producing a composite membrane, comprising:

14. The method according to claim 13, wherein the metal compound film containing a metal different from titanium as a component is made of amorphous silica.

15. The method according to claim 14, wherein the film made of amorphous silica is densified by heat treatment.

16. The method according to claim 13, wherein the titanium alkoxide is at least one selected from the group consisting of titanium tetramethoxide, titanium tetraethoxide, titanium tetraisopropoxide, and titanium tetrabutoxide.

17. The method according to claim 13, wherein the solvent alcohol is at least one selected from the group consisting of methanol, ethanol, and isopropanol.

18. The method according to claim 13, wherein the holding temperature of the reaction solution is 0 or more and 100 or less.

1 9. A composite characterized in that the composite film obtained by the method according to any one of claims 13 to 18 is subjected to a heat treatment so that the titanium oxide is transformed into a crystalline anode phase. Manufacturing method of membrane.

19. The method according to claim 18, wherein the heat treatment is carried out at a temperature of not less than 200 and not more than 100.

2 1. A composite film obtained by the method according to any one of claims 13 to 20, wherein the composite film has a uniform thickness of 0.01 to 100 m, which is bonded to a surface of a substrate. It is characterized by having one or more layers of a metal compound film containing a metal different from titanium as a component, and having a uniform titanium oxide film with a thickness of 0.01 to 100 zm on the outermost surface. And a composite membrane.

2 2. A composite structure having a photocatalytic action, comprising the composite film according to claim 21 in a surface layer.